Creep Analysis Research Articles

Comparative Analysis of Creep in Standard and Fibre Reinforced Concretes under different Load Conditions

The paper presents comparison of creep measurments in normal concrete and concrete modified with dispersed reinforcement - polypropylene and steel fibres (FRC). The tests were performed for two levels of applied load: 40% and 80% of the destructive load at the load time, respectively, at 1, 4, 7 and 28 days. The resulting creep strain was compared with the calculating method from Eurocode 2, and Pre-norm Fib 2010. Significant differences in the results of the creep calculated based on the Code and measured in the research were noticed. It was also shown that the creep of FRC has different development compared to the normal concrete especially under early-age load. The value of proposed creep factor for young concrete calculated based on study results was few times higher than calculated based on the Code. The creep strain of fibre reinforced concrete loaded at the age of 24hours was, moreover much higher than of concrete without fibres. The paper illustrated differences in the dynamics and final values of creep deformation of normal concrete and fibre reinforcement concrete.

Indentation Creep Analysis of Solder Joint considering Cu-Sn Intermetallic Compound

Indentation Creep Analysis of Solder Joint considering Cu-Sn Intermetallic Compound

Creep Analysis of Plain-Woven Laminates Based on a Homogenization Macroscopic Constitutive Model

In this study, creep analysis of plain-woven GFRP laminates based on a homogenization macroscopic constitutive model is conducted. To this end, an elastic-creep macroscopic constitutive model which is able to express strong anisotropy of composites is introduced, and the material parameters in the model are determined based on the results of a triple-scale homogenization method using a unit cell at room temperature (25°C) and elevated temperature (80°C), respectively. Then, creep analyses of plain-woven glass fiber/epoxy laminates are conducted on four uniaxial loading condition, i.e. θ = 0°, 15°, 30° and 45°, using the macroscopic constitutive model and the triple-scale homogenization method at the both temperature. It is found that the analysis results of constitutive model are in good agreement with those of the triple-scale homogenization method.

Beyond Navier–Stokes equations: capillarity of ideal gas

The system of Navier–Stokes–Fourier equations is one of the most celebrated systems of equations in modern science. It describes dynamics of fluids in the limit when gradients of density, velocity and temperature are sufficiently small, and loses its applicability when the flux becomes so non-equilibrium that the changes of velocity, density or temperature on the length compatible with the mean free path are non-negligible. The question is: how to model such fluxes? This problem is still open. (Despite the fact that the first ‘final equations of motion’ modified for analysis of thermal creep in rarefied gas were proposed by Maxwell in 1879.) There are, at least, three possible answers: (i) use molecular dynamics with individual particles, (ii) use kinetic equations, like Boltzmann’s equation or (iii) find a new system of equations for description of fluid dynamics with better accounting of non-equilibrium effects. These three approaches work at different scales. We explore the third possibility using the recent findings of capillarity of internal layers in ideal gases and of saturation effect in dissipation (there is a limiting attenuation rate for very short waves in ideal gas and it cannot increase infinitely). One candidate equation is discussed in more detail, the Korteweg system proposed in 1901. The main ideas and approaches are illustrated by a kinetic system for which the problem of reduction of kinetics to fluid dynamics is analytically solvable.

Creep of Steam-Turbine Diaphragm Under Variable Loading Conditions

The authors put forward a procedure of creep analysis for variable loading conditions, which involves the use of the incremental creep theory and finite element method. Variable loading with load increase and relief at a constant temperature is considered as a stepwise process. The authors study a growth of deflections and stress relaxation in a intermediate-cylinder diaphragm of a steam turbine in various loading modes as well as special features of residual stress distribution in fixed blades.

Creep rupture behaviour of circumferentially welded mod. 9Cr–1Mo steel pipe subject to internal pressure and axial load

The multi-axial creep strength of circumferential welds in power piping, including failure mode and failure life against a wide range of stress ratios and stress levels, was newly examined in this paper. The creep rupture behaviour of modified 9Cr–1Mo steel (9Cr–1Mo–VNb steel; ASME P91) pipe with a circumferential weld subject to combined internal pressure and axial load was experimentally investigated at 650 °C. The test results, with several kinds of stress ratios of macroscopic axial and hoop stress can be summarised as follows. Along with the increased stress ratio (axial/hoop), both failure location and failure mode changed from a base metal failure caused by hoop stress to an FGHAZ (fine-grained heat affected zone) failure due to axial stress. The stress ratio where the failure mode changed was ‘0.8’. Strength reduction in FGHAZ failure by axial stress should be considered in the structural design of circumferential welds. A series of FEM creep analysis was carried out to discuss the relation of the failure mode to both the local stress distribution and the damage. The failure mode variation along with the increase in the stress ratio is also discussed based on simplified ductile creep failure analysis.

Steady state creep behavior of thermally graded isotropic rotating disc of composite taking into account the thermal residual stress

The present paper investigates the steady-state creep behavior of thermally graded isotropic disc rotating at elevated temperature. The composite discs are made of aluminum matrix reinforced with silicon-carbide particulate. The creep analysis is carried out using isotropic Hoffman yield criterion. The stress and strain rate distributions have been calculated for the discs. The creep parameters vary along the radius of the disc and have been estimated by regression fit of the available experimental data. Investigations for disc operating under linearly decreasing temperature from inner to outer radii has been done taking into account the phase-specific thermal residual stress. Further work has been done for discs operating under linearly increasing, parabolically decreasing and parabolically increasing temperatures. The results are displayed and compared graphically in designer friendly format for the above said temperature profiles. It is observed that there is a significant change in the stress distribution due to the presence of thermal residual stress. The radial strain rate is compressive for the discs operating at elevated temperature in the absence of residual stress, but due to the presence of residual stress the strain rate becomes tensile as one gradually moves along the radial distance and again becomes compressive near the outer radius. However, the presence of residual stress led to an increase in the tangential strain rate in the discs as compared to the discs without residual stress. Thus it is concluded that there is a need to extend the domain of thermal gradation in designing rotating discs.

Primary and secondary creep in aluminum alloys as a solid state transformation

Despite the massive literature and the efforts devoted to understand the creep behavior of aluminum alloys, a full description of this phenomenon on the basis of microstructural parameters and experimental conditions is, at present, still missing. The analysis of creep is typically carried out in terms of the so-called steady or secondary creep regime. The present work offers an alternative view of the creep behavior based on the Orowan dislocation dynamics. Our approach considers primary and secondary creep together as solid state isothermal transformations, similar to recrystallization or precipitation phenomena. In this frame, it is shown that the Johnson-Mehl-Avrami-Kolmogorov equation, typically used to analyze these transformations, can also be employed to explain creep deformation. The description is fully compatible with present (empirical) models of steady state creep. We used creep curves of commercially pure Al and ingot AA6061 alloy at different temperatures and stresses to validate the proposed model.

Negative Outcomes of Poly(l-Lactic Acid) Fiber-Reinforced Scaffolds in an Ovine Total Meniscus Replacement Model.

Our objective was to test the efficacy of collagen-hyaluronan scaffolds reinforced with poly(l-lactic acid) (PLLA) fibers in an ovine total meniscus replacement model. Scaffolds were implanted into 9 sheep (n = 1 at 8 weeks, n = 2 at 16 weeks, n = 3 at both 24, 32 weeks) following total medial meniscectomy. From 16 weeks on, explants were characterized by confined compression creep, histological, and biochemical analyses. Articular surfaces were observed macroscopically and damage was ranked histologically using the Mankin score. At sacrifice, three of the nine PLLA scaffolds had completely ruptured, and the intact scaffolds experienced progressive shape changes and severe narrowing in the body region at 16, 24, and 32 weeks. Aggregate compressive modulus and permeability did not improve with time. Histological and biochemical analyses showed significantly less extracellular matrix and less matrix organization compared to native tissue. Osteophytes, bone erosion, and cartilage damage were observed, increasing with time postimplantation. A buildup of lactic acid and/or the rapid loss of scaffold mechanical integrity due to PLLA degradation are probable causes for the joint abnormalities observed in this study. These results are in sharp contrast to those of our previous successful total meniscus replacement studies using polyarylate [p(DTD DD)] fiber-reinforced scaffolds. This suggests that PLLA fiber as produced in this study cannot be used as reinforcement for a meniscus replacement scaffold.

Creep and recovery behavior analysis of space mesh structures

The Schapery's nonlinear viscoelastic theory and nonlinear force-density method have been investigated to analyze the creep and recovery behaviors of space deployable mesh reflectors in this paper. Based on Schapery's nonlinear viscoelastic theory, we establish the creep and recovery constitutive model for cables whose pretensions were applied stepwise in time. This constitutive model has been further used for adjustment of cables’ elongation rigidity. In addition, the time-dependent tangent stiffness matrix is calculated by the partial differentiation of the corresponding load vector with respect to the nodal coordinate vector obtained by the nonlinear force-density method. An incremental-iterative solution based on the Newton-Raphson method is adopted for solving the time-dependent nonlinear statics equations. Finally, a hoop truss reflector antenna is presented as a numerical example to illustrate the efficiency of the proposed method for the creep and recovery behavior analysis of space deployable mesh structures.

Creep analysis of concrete with different mineral admixtures

Creep analysis of concrete with different mineral admixtures

Estimation of longitudinal velocity noise for rail wheelset adhesion and error level

The longitudinal velocity (forward speed) having significant importance in proper running of railway wheelset on track, depends greatly upon the adhesion ratio and creep analysis by implementation of suitable dynamic systemon contamination. The wet track condition causes slip and slide of vehicle on railway tracking, whereas high speedmay also increase slip and skidding to severewear and deterioration ofmechanical parts. The basic aimof this research is to design appropriatemodel aimed estimator that can be used to control railway vehicle forward velocity to avoid slip. For the filtration of disturbance procured during running of vehicle, the kalman filter is applied to estimate the actual signal on preferered samples of creep co-efficient for observing the applied attitude of noise. Thus error level is detected on higher and lower co-efficient of creep to analyze adhesion to avoid slip and sliding. The skidding is usually occurred due to higher forward speed owing to procured disturbance. This paper guides to minimize the noise and error based upon creep coefficient.

Creep analysis of silicone for podiatry applications

Purpose. This work shows an effective methodology to characterize the creep–recovery behavior of silicones before their application in podiatry. The aim is to characterize, model and compare the creep–recovery properties of different types of silicone used in podiatry orthotics.Methods. Creep–recovery phenomena of silicones used in podiatry orthotics is characterized by dynamic mechanical analysis (DMA). Silicones provided by Herbitas are compared by observing their viscoelastic properties by Functional Data Analysis (FDA) and nonlinear regression. The relationship between strain and time is modeled by fixed and mixed effects nonlinear regression to compare easily and intuitively podiatry silicones.Results. Functional ANOVA and Kohlrausch–Willians–Watts (KWW) model with fixed and mixed effects allows us to compare different silicones observing the values of fitting parameters and their physical meaning. The differences between silicones are related to the variations of breadth of creep–recovery time distribution and instantaneous deformation-permanent strain. Nevertheless, the mean creep-relaxation time is the same for all the studied silicones. Silicones used in palliative orthoses have higher instantaneous deformation-permanent strain and narrower creep–recovery distribution.Conclusions. The proposed methodology based on DMA, FDA and nonlinear regression is an useful tool to characterize and choose the proper silicone for each podiatry application according to their viscoelastic properties.

Experimental observation of creep damage evolution in seam-welded elbows of mod. 9Cr-1Mo steel

Seam-welded elbows and straight pipe of the same size as actual high temperature reheat piping for boiler applications were manufactured, and internal pressure creep testing was conducted. Uniaxial creep testing was also performed in order to compare creep damage behaviours. Comparing the observed creep damage evolution and stress analysis results, a creep damage estimation method was discussed. Creep damage distribution varied depending on ovality in the cross sections of the seam-welded elbows. It is important that FEM models for creep analysis incorporate measurement results for the cross-sectional shape of seam-welded elbows. Using the nominal stress of the specimens and the average creep rupture data from small size uniaxial welded joint tests, a simplified prediction method was discussed, which is applicable to creep rupture time prediction for both large creep specimens and seam-welded elbows.

Evaluating long-term performance of Glass Fiber Reinforced Plastic pipes subjected to internal pressure

A computational modeling procedure is developed for simulating long-term creep behavior of Glass Fiber Reinforced Plastic (GFRP) mortar pipes subjected to internal pressure. The modeling procedure includes creep evaluation, stress analysis, failure evaluation and degradation of mechanical properties. Different levels of internal pressure are examined to obtain sufficient data point on failure-pressure versus time-to-failure graph up to 100,000min. At each specific pressure level, the modeling procedure continues till the functional failure is distinguished implying on weepage phenomenon. Obtained data are extended to 50years using extrapolation technique for predicting the remaining strength of investigated GFRP pipe after 50years.

Analysis of Rotating Components Based on a Characteristic Strain Model of Creep

This paper discusses the application of a characteristic strain model (CSM) to analyze the creep behavior of rotating components. First, simple cylinders are analyzed at variable loads and different model constants. A closed-form analytical solution for the steady-state stress and the location of the skeletal point in the rotating solid cylinder are obtained. Then, the hollow cylinder behavior is investigated by numerical analysis, and the skeletal point location is shown to be independent of the applied load. Finally, a numerical creep analysis of a steam turbine rotor is carried out with a detailed examination of the stress and creep strain fields in the rotor disk. The existence of multiple skeletal points in the rotor disk, as well as the independence of their locations of the creep data, is shown.

Fe Analysis of a Steam Turbine HP Rotor Blade Stage Concerning Material Effort, Dynamic Properties and Creep Damage Assessment

Abstract This paper is concerned with the 1st stage of HP rotor blade assembly steam turbine TK 120. The methodology was focused on the selection of mechanical properties and the way of the rotor disc modeling and estimating the degree of damage caused by creep. Then the dynamic interference between the frequencies of excitation and the natural frequencies was assessed. Static calculations were performed for the cyclic sectors consisting of the disc, disc blades, spacers and shrouding, including loads as temperature, mass forces from the angular velocity and the pressure on the blades. Then, the creep analysis using a Norton’s model and the modal analysis were performed. Static analysis gave information concerning the distributions of displacements, stress and strain components. In the creep analysis, the creep displacements and stress relaxation versus time were determined and the estimated degree of damage caused by creep was evaluated at each part of the rotor disc. In the modal analysis, the natural frequencies and modes of vibrations corresponding to the nodal diameters were found. The results of modal analysis were shown in the SAFE graph. Numerical calculations have shown that the rotor disc was a well-designed structure and did not reveal any dynamic interference.

Non-linear Creep Analysis of Ceramic Specimen Using Finite Element Method

In the present work the stress analysis of a ceramic tensile specimen is obtained. The effects of specimen geometry along with the pin loading are considered in the stress distribution calculations. Thereafter, the optimization based on a set of constraints is performed on the specimen with pinhole location, pinhole diameter, head width, neck radius and gauge length as its design variables. The work is then extended for the non-linear analysis for creep. A mathematical model is developed which is implemented using C++ code.

Statistical analysis and modelling of in-reactor diametral creep of Zr-2.5Nb pressure tubes

This paper presents the development of a simplified regression approach for modelling the diametral creep over time in Zr-2.5wt% Nb pressure tubes used in CANDU reactors. The model is based on a large dataset of in-service inspection data of 328 different pressure tubes from eight different CANDU reactor units. The proposed weighted least squares (WLS) regression model is linear in time as a function of flux and temperature, with a temperature-dependent variance function. The model predicts the shape of the observed diametral creep profiles very well, and is useful not merely for prediction, but also for assessing tube-to-tube variability and manufacturing properties among the inspected tubes.

Practical considerations of the use of cross-weld and compact tension specimens’ creep data

This article gives an overview of the use of cross-weld and compact tension specimen modelling and analyses data to characterise creep behaviour of the high-temperature components. Cross-weld and compact tension specimens are used to describe creep crack growth in heterogeneous material structures, such as welds, and a number of factors that affect the creep behaviour of the structure, associated with this heterogeneity, have been identified. Creep data obtained from cross-weld specimen modelling are substantially affected by the material model used (e.g. Norton power law, Liu-Murakami), stress singularities that arise at the material interfaces and in between the columnar and equiaxed zones of the weld material, residual stresses which arise through the thickness of a multi-pass weld and the extraction orientation of the specimen relative to the welding direction. Creep crack growth data obtained from compact tension specimen testing and analyses are strongly dependent on the material models used (isotropic hardening models, Norton creep law, Liu/Murakami model, etc.), the path dependence of the C*-contour integral fracture parameter for certain heterogeneous material configurations and the accurate computation of material constants for damage mechanics models and the agreement between loading state to the actual stress state of the component to which the compact tension specimen creep data are applied to. This study examines typical results and observations from cross-weld specimen and compact tension specimen creep analyses, identifying the advantages, disadvantages and limitations of each specimen procedure.